This invention relates generally to a cutting or milling tool and method for cutting or milling fixed multiple casing strings downhole, and more particularly to such a cutting tool and method having cutting blades swinging radially outwardly from the cutting tool for cutting the casing strings.
Heretofore, such as shown in U.S. Pat. No. 4,887,668 dated Dec. 19, 1989, cutting tools for cutting well casing or casing strings have been provided utilizing swinging blades for first cutting the inner periphery of a string of well casing and then cutting a section of the cut casing string from its annular cut end for removing a desired length or longitudinal section of casing as might be required for removing a damaged section or to provide a window for diagonal drilling, for example. Swinging blades heretofore as shown in the aforementioned patent have had separate cutting inserts or discs mounted on their outer ends and upper sides for cutting a single string of casing.
Normally, and especially for wells of a substantial depth, casing strings of different diameters are utilized with the lowermost casing string being of the widest diameter. For example, an outer lower casing of around 133/8 inches in diameter with an inner upper casing of around 95/8 inches in diameter may be utilized with overlapping end portions providing an annulus filled with concrete for securing the two casing strings together in a sealed relation. Thus, in the event the removed casing sections include a so-called cemented joint, it is necessary to remove two separate casing strings at the joint as well as concrete in the annulus between the strings.
In the event the inner casing is removed first in one cutting operation, and then the outer casing is removed in a separate cutting operation a different blade or tool is utilized which requires a tripping or removal of the tool from the bore hole. If the same cutting tool is used for both cutting operations, it is difficult to stabilize the cutting tool during cutting of the outer string as the tool body which fits within the inner casing is spaced laterally a substantial distance from the inner periphery of the outer casing. While special blades utilizing a tang or projecting lug on the lower end of each blade for riding along the inner periphery of the outer casing may be used for stabilization of the tool during the cutting operation, such an arrangement requires removal of the cutting tool from the bore hole after cutting of the inner casing for attachment of the special blades and subsequent running in of the tool. Such a "tripping" of the cutting tool is costly and time consuming.
U.S. Pat. No. 3,331,439 shows a cutting tool for cutting multiple casing strings simultaneously without having to remove the cutting tool from the well bore and with the cutting tool centered by the small diameter casing being cut. However, this cutting tool removes a section or length of casing by engaging and cutting the lower annular cut end of the casing and the cutting surface of the blade is along its upper side only.
For cutting multiple casing strings simultaneously, the cutting blades must first cut through the walls of the multiple casing strings in series, and then a section or length of the multiple casing strings is cut away simultaneously. Thus, as shown in U.S. Pat. No. 3,331,439, the cutting surface on the extending end of the pivoted blade has been utilized for cutting through the casing walls in series and then the cutting surface along the upper side of the blade has been utilized for cutting away the lower annular cut ends of multiple casing strings simultaneously during upward movement of the cutting tool.